As Luke says in an answer to this question, a species may never attempt space travel if they cannot see that there is something out there.

My question is just this; is that possible? Could a planet/solar system be wrapped in something that prevents the light of other stars from reaching the species? Could this be done without an artificial structure, such as that of the planet Krikkit? Assume this system has only the one planet orbiting the star, so the species doesn't try to go somewhere else in the system.

$\begingroup$Venus! Then one day it rains, and everyone freaks that the sky is falling.$\endgroup$
– Mirror318Jun 27 '16 at 22:53

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$\begingroup$No planets can see stars... They don't have eyes! But seriously, "Mote In God's Eye" has a relevant situation, where the system is inside a giant nebula.$\endgroup$
– Nathaniel FordJun 28 '16 at 1:00

19 Answers
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Perpetual cloud cover -- such as what you might find on Venus -- would of course obscure the night sky and the stars therein. The caveat here is that you would likely have people wondering "What's beyond the clouds?", and if any of those happen to get through them during the night they'd see the stars and then -- potentially, anyway -- cue the space race.

Light

It's well known that we can't see the stars (save for our own sun, which is of course a star itself) during the day. This is because the sun is so bright that it simply obscures the stars from view. At night, however, our own planet blocks the sun's light and allows us a view of the stars above.

We can see the stars at night because our moon doesn't reflect back enough of the sun's light to obscure the stars. This is because its albedo is only ~12%. However, if our moon were "brighter" -- say, closer to Saturn's moon Enceladus's 99% -- it could conceivably reflect enough light back toward the planet to make the night sky almost as bright as the day's, enough so to obscure the stars from view.

This would require a planetary system where the moon doesn't go through phases -- i.e. it orbits the planet at precisely the right period to keep it on the opposite side from the sun, but is never eclipsed (though as Sean Raymond points out in comments this is probably impossible, as this would pretty much have to put it in the L2 Lagrange point, which is unstable) -- or where there are multiple high-albedo moons orbiting in such a way that there is always at least one moon (or combination of two or more) bright enough to obscure the stars from view.

Alternatively, a binary (or more) solar system might be configured in a way that there's always at least one sun filling this role of obscuring the "night" sky and its view of the stars.

But wouldn't a moon give the inhabitants reason to want to head into space? It might, but on the other hand remember that we're talking about moons that are nearly as bright as the sun itself, which makes direct observation very very difficult (unless you like your retinas burned off). Without direct observations, determining that the moons are something that could be visited would be fraught with unique difficulties, to say nothing of the fact that there's no observable universe for the inhabitants to see and from that to derive relative scales, such as the sizes and distances of their moons and sun; they may never even arrive at concepts such as "orbits", something we were able to figure out after millennia of studying the other planets in our solar system.

Now, granted, you might be able to make some observations of a crescent moon, but the same high albedo that obscure the stars themselves would likewise obscure the "dark side" of the moons. Still, the fact that the moons go through phases while the sun doesn't will naturally drive curiosity and could indeed lead to someone figuring out that they're orbiting bodies they might be able to reach, but again without any concept of relative scale derived from observations other bodies, to say nothing of the complete absence of even a rudimentary grasp of orbital mechanics, the challenges in actually getting out there may prove insurmountable, or at the very least dissuade anyone who might have been capable of surmounting them.

$\begingroup$The idea of the Moon not going through phases is unfortunately not dynamically stable. It corresponds to a Moon being at the L2 Lagrange point, which is an unstable equilibrium. As for a many-star system in which one star is constantly illuminating a planet's surface, here is one example in that direction: planetplanet.net/2016/03/23/…$\endgroup$
– Sean RaymondJun 27 '16 at 18:58

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$\begingroup$Multiple very reflective moons could probably have an arrangement where at least one of them is on the night side at all times.$\endgroup$
– KevinJun 27 '16 at 20:45

$\begingroup$Ok, so they cannot see stars but they can see the moon. That didn't really solve OP's problem.$\endgroup$
– Tomáš ZatoJun 28 '16 at 8:38

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$\begingroup$Telescopes were not created to look up, they were created to see distant objects on the ground. You can see some bright stars (and planets) during the day through a smallish telescope. It would not likely take long for someone to look up and see a star.$\endgroup$
– AstroDanJun 28 '16 at 13:32

$\begingroup$While a good solution, it begs further questions, such as: Could a star form within this (or a comparable) supervoid? (After all, there's bound to be a reason every known star is within a galaxy, isn't there?) And if it could, would there be enough matter to coalesce into at least one planet? And if so, would conditions be right for life to arise on this void-bound planet? I certainly concur that with an empty night sky we'd be unlikely to develop tools to peer further into that inky blackness, so if my other concerns are moot then +1.$\endgroup$
– KromeyJun 27 '16 at 21:44

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$\begingroup$@Kromey Perhaps the star and its planet formed at the edge of a galaxy and got slingshotted out of the galaxy after a near miss with a larger star. Or, Wikipedia suggests galaxies colliding: Intergalactic star.$\endgroup$
– Molag BalJun 28 '16 at 3:38

$\begingroup$This is an interesting idea. There is a category of stars called hypervelocity stars (cfa.harvard.edu/oir/sp/hypervel.html) that are in the process of being ejected from the Milky Way. If those stars can retain their planets, then a few billion years in the future they may be pretty lonely places!$\endgroup$
– Sean RaymondJun 28 '16 at 9:23

$\begingroup$@amaranth Excellent point, hadn't considered a star ejected from its galaxy. Obviously solves my qualms about how it could form, so I'm firmly +1 on this idea now.$\endgroup$
– KromeyJun 28 '16 at 14:32

$\begingroup$Are you sure galaxies wouldn't be visible from 0.9GLY? Keep in mind that species that develop on such a planet would probably evolve phenomenal night vision.$\endgroup$
– imallettJun 28 '16 at 18:16

Short answer is universal expansion. Humans today live in a very unique point in the history of the universe as we can see and speculate both what happened in the past and what will happen in the future.

One of these future predictions is that the as the universe expands it will begin to expand faster than light. This will make it impossible for light to ever reach another galaxy or star system. The light will travel continously never reaching anything beyond the galaxy it exists in or even the solar system itself. Your planet could exist trillions (upon trillions) of years from now where this is happening and any evolved form of life would see empty space outside of their home system.

I would look up kurzgesagt on youtube and watch some of his space videos as in one of them it explains this faster than light expansion and probably explain it better than I can.

Edit: Here's the video. It talks about humanities own limits but it could be applied to your situation. You would just need a lonely star system.
https://youtu.be/ZL4yYHdDSWs

Locating the planet within a Dark Nebula

Figured I would jump in and give an astronomical option.

Dark nebula are absorption nebula that can stretch for many light-years. They are so dense that only deep infrared and radio emissions can penetrate the outer layers. However because of their density star formation occurs in the center. The star will carve out a "bubble" of clear space surrounded by an opaque cloud. From this bubble the people would only be able to see other stars if they tried extremely hard. It also seems likely that they would develop a philosophy regarding themselves as the center of the universe and trying to disprove this would be even more taboo then it was on earth.

$\begingroup$This idea is not dissimilar to the planet Krikkit in the Hitchhiker's Guide to the Galaxy series.$\endgroup$
– Michael SeifertJun 28 '16 at 13:53

$\begingroup$@MichaelSeifert I had forgotten about that but the cases are very similar. If I recall correctly it took outside intervention for the Krikkit to develop space travel. If that can be avoided then they should stay nicely bottled up.$\endgroup$
– AstroDanJun 28 '16 at 13:58

$\begingroup$The nebula that enclosed Krikkit was also artificial (the OP notes this example in their question), but it's good to know that such a case might also arise naturally.$\endgroup$
– Michael SeifertJun 28 '16 at 14:01

Ice could be an option. You could have an ocean planet with a thick layer of ice covering everything. If the planet has a hot, rocky core with thermal vents, that could provide the energy necessary for life, with microbes living directly off of the warmth from the core, tiny animals living off of colonies of microbes, and larger animals living off the smaller animals.

$\begingroup$Europa and Enceladus are examples of this in our own solar system, so there are probably a huge number of other examples just in our galaxy$\endgroup$
– trichoplaxJun 27 '16 at 21:20

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$\begingroup$I like this idea! If life were underwater (or under ice) then the inhabitants would be removed not only from the heavens but even from the planet's surface. FYI this type of world could be very common. See here: aeon.co/essays/… and here: planetplanet.net/2015/06/04/…$\endgroup$
– Sean RaymondJun 29 '16 at 9:42

Planetary rings not only would directly block the the vision of a lot of stars along the Equatorial zone.
Would also reflect bright lights from the sun on the rest of the world making every star invisible.

$\begingroup$Would rings suffice, though? It seems like latitudes that were north/south enough wouldn't be able to see the rings, nor the light they reflect, nullifying their effect and revealing the night sky and its glorious stars!$\endgroup$
– KromeyJun 27 '16 at 21:22

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$\begingroup$In real life, rings are not very bright. I think you could see the stars around the rings even from the equator on a planet with rings anything like the ones found in our solar system.$\endgroup$
– Peter CordesJun 27 '16 at 22:13

$\begingroup$@Kromey If you combine rings with your suggestion of very high albedo satellite, it should work? The rings would have been created by the recent breakup of something with proper composition. Or cryovolcanism on a small very bright moon. Reasonably such would be needed for a moon to have high albedo permanently and if the moon was small enough some of the ice would escape its gravity and create a bright ring on the same orbit. Might still need more than one moon...$\endgroup$
– Ville NiemiJun 27 '16 at 22:26

$\begingroup$@VilleNiemi no, you can't have a ring at the same orbit as a moon. If you're really lucky, you might get a second and third body in L4 and L5 of the original moon, but that's not nearly enough to outshine the stars. As of what would happen to the ice of a cryovolcano, I would guess the only three real options are fall onto the planet / back onto the moon / out into space.$\endgroup$
– John DvorakJun 28 '16 at 5:49

$\begingroup$@JanDvorak Rings are not permanent. It is about the process replenishing material being in equilibrium with the rings dispersing or in this case with the material falling back to the moon. So there would be a ring if the cryovolcanism lasted long enough until the cryovolcanism is reduced below the threshold needed to maintain the ring.$\endgroup$
– Ville NiemiJun 28 '16 at 9:34

Well the first and most obvious answer is light pollution. If an alien species were to use an extremely large amount of artificial light for everyday/night activities, they wouldn't see the stars. Same goes for if they happened to live on a planet with an extremely reflective surface. For example, if you lived on a planet whose year was the same length of its day, one side would always face its sun; thus life would have to live on that side of the planet (since it needs the sun for energy), and its planet would always reflect enough light to cause light pollution.

Another possible cause is clouds. If a species were to live on a planet that was always covered in a layer of gas, they may not be able to see past the clouds and realize that there were stars.

Finally, though this doesn't have much to do with the planet but moreso the species, evolution. Just as on Earth we have species that have evolved to not have eyes, so could be the case with an intelligent life form on another planet, which would cause a lack of interest in exploring what one cannot see.

$\begingroup$Long before there's too much light pollution from artificial lights, there'd be plenty of dark nights for stargazing, so even if they can't be seen now these folks would still know the stars are out there...$\endgroup$
– KromeyJun 27 '16 at 18:29

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$\begingroup$Well, superstitious old hillbillies might still believe in stars and fairies and spirits and other nonsense, but sophisticated and educated folks like us know there's no such thing.$\endgroup$
– Josh DavisJun 27 '16 at 19:38

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$\begingroup$I like your idea of a civilization on the sun-facing side of a tidally locked planet. However, you need a really serious obstacle to just sailing or walking around to the other side of the world, because people will go even if it's difficult. Some of them especially because it's difficult.$\endgroup$
– Peter CordesJun 27 '16 at 22:48

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$\begingroup$@JoshDavis -- you forget that pilots get a pretty darn good view of the night sky...$\endgroup$
– ShalvenayJun 28 '16 at 2:18

$\begingroup$@PeterCordes frigging cold (which is much colder than freezing cold) is a pretty serious obstacle. Though, that didn't discourage 1 person in a billion to live there on Earth.$\endgroup$
– John DvorakJun 28 '16 at 6:04

A sentient species could possibly also never develop the ability to see at all, which would make sense especially for planets in dark zones of their star system. In this case, they would simply not see that there are any stars around them and just deal with their own surrounding without having any idea that there might be anything beyond.

$\begingroup$If the species was technological, they would eventually discover electromagnetic radiation regardless of having any sensory organs to detect it. If any EM radiation is coming from the sky, they would probably eventually detect it. (Maybe in a way similar to Wilson & Penzias's Nobel-winning discovery of cosmic background radiation). After that, upward-looking instruments in all possible wavelengths would eventually be built, leading to the conclusion that something was up there.$\endgroup$
– Peter CordesJun 28 '16 at 5:53

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$\begingroup$@PeterCordes I agree that this will happen most likely eventually, but this would be true for most of the other answers given here. So another question might be if there could be any sentient species that maybe never reaches the point of discovering EM radiation. And I can imagine that being possible, considering that there is likely a vast amount of civilizations out there. After all, it might be possible that there is also some "space feature" that we can't sense (and therefore have not discovered) that might be totally obvious to other species that can easily sense it.$\endgroup$
– mdominoJun 28 '16 at 10:59

$\begingroup$Hmm, yes, that's a good point. radio-astronomy can see through clouds or constant illumination, so this argument applies nearly universally.$\endgroup$
– Peter CordesJun 28 '16 at 12:14

You could make the planet's air be turbulent and tend to be full of dust.

If it never calms down enough for the dust to fully settle, you'll still get sunlight diffused through, but starlight won't make it.

But it gets better. The constant wind and dust would make it difficult to construct and maintain the sensitive optics needed to look at the stars in the first place. Made a giant glass lens? It's scratched up and useless within a month. If you put a clear pane of glass in front to protect the lens, that pane gets scratched up instead, and you have to replace it frequently. Maybe one night the wind calms down enough that you could actually see stars, in theory. But you can't be sure if those specks of light are from the sky, or reflections off some bits of dust on the end of your telescope. By time you clean the lens off, the wind has picked back up.

And if there's always dust in the air, visibility will always be limited to within a few miles or less. Which means your aliens' eyes won't need to be able to pick out details at a great distance, because such an ability would not provide a survival advantage. With less visual acuity, your aliens wouldn't even notice the pinpricks of light from distant stars on the rare occasions where starlight would make it to the surface. And the same problem which prevented them from evolving sharp vision would also make telescopes much less useful, which means they might never invent high magnification optics for looking at distant objects.

$\begingroup$I don't think miles of visibility implies that poor visual acuity wouldn't evolve. There are a LOT of things worth looking at within 100 meters. Such a society could use microscopes, but might not invent them easily if optics other (and especially telescopes) weren't as useful.$\endgroup$
– Peter CordesJun 27 '16 at 22:52

A companion star of the primary

In Asimov's 1941 short story Nightfall, he imagines a planet that is always illuminated by companion stars of the primary.

I don't think this could be a plot point for a civilization to never attempt space travel. Even in the times where the Earth was flat and heavens were only accessible through death, Earthlings tried to build as high as possible; climb as far as possible. So I think a civilization will eventually try space travel even if they cannot see the stars.

The only thing I can come up with is distance. You should be so far from every star that light goes through either redshift of blueshift, becoming invisible to the naked eye.

Not sure if it's a really huge distance, or some thousand light years are enough (which is still quite huge), but thinking about isolated planets might be a good start for you - well, depending on your setting.

$\begingroup$Can you please post some of the relevant information here? While the linked material may answer the question, we generally expect that you include a little more in an answer.$\endgroup$
– HohmannfanJun 28 '16 at 20:26

External Influence

Noone has mentioned interference from an external party.

Imagine that the planet is a wildlife preserve, to protect a developing civilisation from early contact, or as a science experiment to see how evolution works, or simply as a cage to keep the contents safe from predators.

A philanthropist group of rational and intelligent beings could see fit to raise a "fence" or protective shield that hides the planet, or works to obscure the outward signs of intelligent life. As a side effect, the shield stops all inbound radiation (perhaps uses inbound solar energy as a power source and then presents a "fake" light source on the inside, or acts as a giant diffuser for light to hide the concept of a light source rotating.

The technology to raise such a shield is beyond Humanity at this time, but an external culture could have any level of tech that you want to imagine.

And as a twist in the tail....

it could be that intelligent creatures "taste" better so the whole planet is a farm for raising tasty snacks. The shield is a fence to keep out poachers or any police just as much as keeping the animals inside.

Light Pollution.

In urban areas in our real Earth (though you might want to ask over on the Skeptics SE whether our Earth is the real Earth), it's much harder to see the stars than it is out in areas away from the cities. Sure, it's possible to see stars, but there are so many more, plus the brush of "milk" that gives our galaxy its name, which you need to leave the city to see. In theory, if you have one massive city that covers your planet with lights bright enough (considering that there are still visible stars in NYC you'd need to go even brighter than that), you could block out every single star's light from entering the atmosphere.

Imagine a denser version of The Great Rift in the Milky Way. The space dust wouldn't need to be actually in their star system, but perhaps they have planets out about as far as the Jovian planets whose orbits sweep some of the dust out of the system, but not enough for the planets to be seen.

$\begingroup$My answer is very similar to one that was already given: worldbuilding.stackexchange.com/a/45583/3229 I didn't notice until I posted mine. There is some difference between them, so I'll leave mine here.$\endgroup$
– TecBratJun 29 '16 at 14:12

You can have a planet where nobody can see stars until a fairly high technology level is reached.

About four billion years ago, two stars in a galaxy passed very close to each other and exchanged momentum. One was accelerated beyond galactic escape velocity.

Time passes. Planets form. Life evolves. It becomes intelligent and looks up at the sky. It sees a few planets, and a few very faint fuzzy blobs. This is the view from a solar system deep in inter-galactic space.

Eventually they point powerful telescopes at the fuzzy blobs and see galaxies made of what looks like glowing dust. I wonder how long it takes them to work out that each speck of dust is a sun like theirs?